Update changelogs from fern repo (#5306)

Co-authored-by: dsinghvi <10870189+dsinghvi@users.noreply.github.com>

Author: fern-support

fern/products/sdks/generators/csharp/changelog/2026-05-01.mdx

@@ -1,3 +1,8 @@
+## 2.65.0
+**`(feat):`** Generate CONTRIBUTING.md for C# SDKs, matching the pattern used by the TypeScript generator.
+The file is skipped for whitelabel SDKs.
+
+
 ## 2.64.2
 **`(fix):`** Dedup auth-derived headers in the generated client constructor when
 multiple auth schemes resolve to the same HTTP header name (for